I wonder if that is part of salvific truth. I’m not sure Jews in the OT knew much about the operation of the Trinity. You know? And if the issue was make or break, one would expect a fuller treatment in the biblical texts.

The OT Jews recognized YHWH as the one and only true God. They could have known about the Deity of Messiah from several verses, but this was not the light they has or needed. We have progressive revelation, the full and final revelation in the NT/Christ. Now, salvation is in His name alone (so Jews, Muslims, Unitarians, JWs, Mormons, etc. must trust the real Jesus who is YHWH in the flesh, not a counterfeit christ as creature only…2 Cor. 11:4; Jude 3; Gal. 1:6-9).

Understood, and I think that is a valid frame of reference. I also think people can make a good case that revelation is not progressive and say that this is not a salvific issue. I think rational people can disagree, and I don’t see Yahweh as making the Trinity a deciding factor without it being a bigger factor in the NT, where they would have to convince Jews of this who would be hostile to this belief.

Christians had a pre-theoretical understanding of the trinity, an experiential one, that was not formalized in more details until later heretical attacks necessitating creeds and Councils.

Christians were known for worshipping Jesus as Lord, God. I would not make articulation of the trinity salvific (so Oneness/modalists could be saved in worshiping Jesus as God, but not Arians/Unitarians, etc.), but the Deity of Christ. Muslims deny the Deity, death, resurrection of Christ. This is germane to the gospel and cannot be denuded on any point (IMHO).